The elucidation of the mode of interaction of phospholipid vesicles, as membrane models, with metal ions, and various coagulation proteins, and the manner in which these interactions lead to activation of zymogens which participate in formation of the blood clot has been a long-term objective of this laboratory. To continue to develop this area, we will determine the manner in which monovalent and divalent cation binding sites interact with each other and with the active site in activated protein C; an enzyme which is a potent anticoagulant. A powerful combination of physical and chemical techniques, such as NMR and EPR, will be employed to address these questions, and these will be extended by the preparation and characterization of highly specific chemical agents, monoclonal antibodies, to label and identify the portion of the protein which is involved in its many functions. Advantage will be taken of a form of protein C, "Gla-domainless"-protein C, which lacks many of the cation binding sites of native protein C, to assess structure-function relationships of this protein. Similar studies will be conducted with blood coagulation Factors IX and X. The activation of Factor X, by a multi-protein complex, also containing calcium and phospholipid, is a central event in the clotting of blood. In order to define the mechanism of this process, we will investigate conditions, both physically and kinetically, under which optimal activation occurs. These approaches will again be extended by the preparation and characterization of monoclonal antibodies, which may inhibit or accelerate certain steps in the process, the identification of which will greatly aid our understanding of this system. There is currently a great deal of interest in the factors which control thrombosis and hemostasis and their elucidation at the biochemical level will certainly suggest means of manipulation of this system to the advantage of man.